This invention relates to an improved electrostatic recording material, particularly to an electrostatic recording material which comprises a dielectric layer and an electroconductive transparentized base sheet supporting the dielectric layer.
The electrostatic recording system has recently been widely applied to a facsimile or a computer input-output system suitable for high speed recording in a high speed telecommunication system, a high speed graphic reproduction system, etc. The electrostatic recording material as a recording medium basically comprises a highly dielectric layer, which serves as an electric-charge-retentive layer, and an electroconductive base sheet which supports the dielectric layer. Electrostatic images of electrical signals formed on the dielectric layer are made visible with a developer comprising a toner and a carrier which has a polarity opposite to the polarity of the electrostatic image charge, and fixed as permanent visible images by further treatment.
The electrostatic recording system does not involve any photoelectric conversion in the process of forming electrostatic latent images on the dielectric layer. The electrostatic recording material of the invention, therefore, does not include any so-called photosensitive element.
There have been proposed various methods for forming electrostatic latent images on a dielectric layer. Among them there are a method of imparting electric signals on the dielectric layer by making it contact with an electroconductive material such as a metal; a method of transforming electrostatic latent images formed on the other medium to the electrostatic recording material, which is known as the "TESI" method and disclosed, for example, in PHOTOGRAPHIC SCIENCE AND ENGINEERING, Vol. 9, No. 1, January - February 1965; and a method of forming discharged patterns on the surface of the recording material with use of a photoconductive film as a switching element, which is known as the "WALCUP" method and disclosed, for example, in U.S. Pat. No. 2,833,930. The electrostatic recording material described can be used in any of those methods for forming electrostatic latent images.
The electrostatic recording system described, however, is distinct from the system for forming latent images by photoelectric conversion with the utilization of a photosensitive material in the recording sheet.
In the electrostatic recording system, it is very difficult to obtain multiple reproductions at one time. Therefore, the recorded electrostatic recording material is often used as a master copy for obtaining further multiple copies. In another case, a multiplicity of the electrostatic recording papers recorded with a facsimile or printer plotter are piled and used as a so-called overlay paper. To prepare the electrostatic recording material which is used for those purposes, commercially available tracing papers or glassine papers have been generally used as base sheets. However, such conventional base sheets involve some fatal disadvantages when used for the electrostatic recording material.
To obtain tracing paper or glassine paper having a desired transparency, beating of pulp must be carried out to an utmost extent until cellulose fibers are extremely fibrillated. Consequently, the fibers are injured to impair the paper making property and the physical strength of the paper obtained is unsatisfactory. In addition, since many hydroxy groups which are sensitive to moisture or water are exposed on the surfaces of the fibers as a result of a high fibrillation, the paper becomes well adsorptive of water and accordingly the dimensional stability of the paper is extremely degraded. Owing to those disadvantages, the workabilities for coating and processing in the manufacturing of the electrostatic recording material are significantly lowered. Moreover, the electrostatic recording material produced with use of the above conventional base sheet tends to curl by a change in moisture of the atmosphere or in contact with water and tends to be brittle during the process of fixing treatment with heat. These also lead to make difficult to handle and lower the workability. The above conventional tracing papers and glassine papers further have such a disadvantage that the adsorbed water which is combined with hydroxyl groups is vaporized and expanded for form bubbles in the paper when it is heated, which is the so-called blister phenomenon.
An object of the invention is to provide an improved electrostatic recording material in which the above disadvantages can be avoided.
Another object of the invention is to provide an electrostatic recording material having a high transparency which can be used as a master copy or an overlap paper for duplication.
Other objects and advantages of the invention will become apparent from the following detailed description.